The subject of the invention is a method and a device for heating up liquids in particular for heating up water quickly or for generating steam. A method of heating up liquids characteristic in that the liquid is introduced into the working chamber of an electromagnetic reactor or an induction boiler with a changeable elecromagnetic field, which is filled up to the level of 100% of its volume with fine ferromagnetic elements, where once the electromagnetic reactor or the induction boiler is turned on the liquid is heated up to the desired temperature and subsequently pumped out or blown through or released gravitationally to the receiving device.